小白再看一篇关于全球价值链的文献，有一段实在看不懂：There is an intertwining of i) trade in parts and components; ii) international movement of investment in productions facilities, training, technology and long term business relationships; and iii) demand for services to coordinate this dispersed production, especially infrastructure services such as telecoms, internet, courier, air cargo trade related finance, customs clearance etc.
这个i 、ii 和iii代表什么意思呢？求各位大神指教！